In a long term evolution (LTE) system, a conventional antenna array has a fixed downtilt in a vertical direction, to be specific, the conventional antenna array provides a fixed beam for each user equipment in the vertical direction in a cell. To increase a cell edge user throughput and a cell average throughput, a three-dimensional (3D) beamforming (BF) technology is introduced. Based on an active antenna system (AAS), the 3D beamforming technology may generate beams with different downtilts for user equipments in the vertical direction based on locations of the user equipments, and perform beamforming in both a horizontal direction and the vertical direction. To support the 3D beamforming technology, corresponding channel state information needs to be fed back. The channel state information includes a channel quality indicator (CQI), a precoding matrix indicator (PMI), a rank indicator (RI), and the like.
Generally, the channel state information is obtained through channel estimation by the user equipment. In a conventional channel estimation process, the user equipment measures a reference signal (RS), also referred to as a pilot signal, for example, a channel state information-reference signal (CSI-RS), to estimate channel state information in a horizontal dimension and report the channel state information to a base station. However, for the 3D beamforming technology, the user equipment further needs to perform channel estimation on a channel in a vertical dimension in addition to channel estimation on a channel in the horizontal dimension. Obviously, the conventional channel estimation method only supporting channel estimation in the horizontal dimension is not applicable to the 3D beamforming technology.
Therefore, how to provide a channel state information feedback method is really a problem urgently to be resolved in the industry.